Lithium is a chemical element belonging to the alkali metal group and is soft, silvery-white, and corrosive. Lithium is an increasingly valuable metal for use in alloys for heat transfer applications, rechargeable batteries, and the like. A conventional procedure for the production of lithium metal includes crystallization of lithium chloride from an aqueous concentrated solution of lithium chloride, then electrolysis of molten lithium chloride from a eutectic mixture containing 43 to 46 wt. % lithium chloride and 54 to 57 wt. % potassium chloride. The eutectic mixture melts at 352° C. and thus requires use of materials that can withstand high temperatures in a corrosive environment. The molten-salt electrolysis process is a high-temperature process, which has high energy consumption, requires high production costs, and has a significant effect on the environment. The lithium metal resulting from the molten-salt electrolysis process typically contains impurities such as sodium and thus cannot be used in battery applications.
Lithium metal has also been produced in an electrolysis cell under an inert atmosphere at about room temperature. The process includes dissolving a lithium salt selected from LiTFSI, LiCl, LiF, LiPF6, and LiBF4 in a conductive non-aqueous solvent. The non-aqueous conductive solvent contains a bis(trifluoromethylsulfonyl)imide (TFSI) anion and may comprise at least one compound selected from 1-butyl-3-methyl-pyridinium bis(trifluoromethylsulfonyl)imide, 1-methyl-propylpiperidin-ium bis(trifluoromethylsul-fonyl)imide, and 1-ethyl-3-methyl-imidazolium bis(trifluoro-methyl sulfonyl)imide. The lithium salt is dissolved in a maximum amount of 30 wt. % with respect to the total weight of the solution. Re-oxidation of reduced lithium is avoided by the absence of an oxygen atmosphere. The foregoing process provides lithium metal that is plated onto the cathode and that contains impurities. Purification of the lithium metal is performed by heat treating the deposited lithium at 800 to 900° C. for 30 to 90 minutes in an inert gas atmosphere.
The foregoing processes are difficult to conduct in a large scale industrial process and/or high temperatures, typically well above 100° C., to produce lithium metal. Also, a subsequent purification step is often required to produce lithium with a purity of greater than 95 wt. % Accordingly, what is needed is a low temperature process that produces lithium metal with purities that are suitable for battery and other applications without the need for a subsequent purification step.